All You Need To Know About Chlorine For Your Hot Tub

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With so many questions and as many different answers about chlorine use in hot tubs, it’s time to set the record straight. This subject is shrouded in misinformation, so let’s put the rumors to bed.

Not All Chlorine is Alike

We don’t recommend packaged chlorine as a primary sanitizer in the hot water of spas, but one type, Dichlor Granular Chlorine, dissolves quickly and is very good for occasional shocking.

Not all chlorine is the same, so let’s look at the differences.

Sodium Dichlor Granular Chlorine (granular spa shock)

Dichlor is the only packaged chlorine suited for spas. While it’s a little more expensive, it has near-neutral pH and does not require adding a cyanuric acid stabilizer. We recommend it as an occasional shock, since it is not available in tablet form, like bromine.

Dichlor in bottle cap
The only kind of chlorine that should go anywhere near your spa!

As mentioned, dichlor has a near-neutral pH, meaning it isn’t excessively acidic or alkaline in character. Additionally, it does not rapidly deplete at higher water temperatures. If you use dichlor, the quick-dissolving fine granular formulation is the best.

Dichlor in tablet form does not exist. If you choose to use granular dichlor as a sanitizer, more frequent doses, and testing will be required than with bromine tablets or other sanitizer systems.

Dissolving dichlor in a bucket of clean water first, then adding that to the spa water is a best practice. Pouring granules directly into a spa can sometimes cause acrylic surface discoloration from direct contact.

Never mix different spa chemicals together; always add them one at a time.

A Better Way to Chlorinate Hot Tubs

The Saltron Mini Chlorine Generator is an easy-to-install plug-in system for hot tubs. It automatically produces pure chlorine from mineral salts.

Swimming pool owners have enjoyed the benefits of salt water purification systems for years. Why let them have all the fun? With this inexpensive and easy-to-install system, you’ll reap all the benefits too!

Salt system in hot tub
Saltron Mini – Salt system diagram

Affordable and easy to install, the Saltron requires no modifications to the spa itself. Learn more about this amazing system here.

Trichlor (pool tabs)

Another popular form of chlorine you’ll find at pool stores, Trichlor, comes in tablet form and is excellent for pool water treatment. We do not recommend this type of chlorine for spas because it has a higher acidic nature, and generally dissolves too slowly to be effective.

Trichlor pool tablets
Trichlor tablets should be used in pools only.

Prolonged contact with the spa shell can result in bleaching of the color and may even mark it, sometimes causing a permanent ring at the waterline.

The increased acidity can also cause problems with pump seals and heaters. Do yourself a favor and avoid Trichlor in spas.

Cal-hypo (calcium hypochlorite)

This type of chlorine is popular for pool use because, well, it’s cheap. It requires adding a cyanuric acid stabilizer to keep it stable in sunlight. Without this stabilizer, Cal-hypo can lose 95% of its effectiveness in just a couple of hours.

Due to its high calcium and high pH level, deposits tend to form on spa heater parts and plumbing fittings. It may also leave a yucky film or ring at the hot tub’s waterline. Cal-hypo is one of the most caustic forms of chlorine on the market, so keep it away from your spa.

If you are going to use chlorine, dichlor is well worth the few extra pennies in weekly cost.

Sodium Hypochlorite (household bleach)

Do yourself a favor, and keep household bleach away from your spa! Not only is bleach a poor sanitizer at higher water temperatures, it readily affects pH balance and tends to have a much harsher chlorine odor.

bottle of bleach
eau de Javel

Avoid Household Bleach!

Household bleach can easily splash on surrounding surfaces, including your spa cover, and may cause permanent damage. Bleach also dramatically reduces filter life when used for cleaning.

Understanding Free, Combined, and Total Chlorine

Chlorine in spa & pool spa water can be present in two forms – Free Chlorine and Combined Chlorine.

Free Chlorine does the job of killing bacteria and oxidizing contaminants. When you add chlorine to the water, you are adding Free Chlorine.

When the Free Chlorine reacts with contaminants such as oils, bacteria and other organics, it becomes Combined Chlorine (aka, chloramines). Unlike Combined Bromine, Combined Chlorine has little sanitizing ability, and no oxidizing ability.

Combined Chlorine, then, is like a used napkin. Chloramines have a harsh odor, and can cause red eyes and irritation. (You’ll have less chance of these problems if using bromine and can avoid them altogether with an alternative sanitizer).

Combined Chlorine + Free Chlorine = Total Chlorine

So, when Total Chlorine is higher than Free Chlorine, Combined Chlorine is present, and you need to shock your pool or spa.

Shocking with OxySpa non-chlorine MPS shock, or dichlor in an extra-large dose will actually oxidize the combined chlorine and destroy the chloramines. You can test and measure Free and Total Chlorine with our 7-in-1 Test Strips.

test strips
Test strips make water testing easy-peasy!

If you have any questions about chlorine, alternative sanitizers, or anything else hot tub-related, leave your comments below!


  1. My 2 person 160 gallon hot tub has an ozone generator. Does this allow you to use less chlorine or bromine or eliminate the need to shock? If not, how often should you shock? This would make a good topic.


  2. Hi Kevin,

    You’ll find with an ozonator, you can maintain free chlorine/bromine levels using less sanitizer. We still recommend shocking the spa after each use, or weekly if the spa isn’t in use.



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